PROJECT SUMMARY Understanding the specific roles of the cerebral hemispheres for the control of bilateral movement is an important goal of motor control research with implications for rehabilitation of neurological injury, especially stroke. For instance, behavioral studies indicate that individuals with right hemisphere damage (RHD) exhibit a diminished response to bilateral arm training compared to those with left hemisphere damage (LHD). Additionally, those with RHD are less likely to use their more-affected arm alone or bilaterally with their less-affected arm. In order to better understand the peculiar disadvantage suffered by individuals with RHD, this proposal seeks to examine hemisphere-specific deficits in interlimb coordination during bimanual tasks by investigating an empirical phenomenon known as interlimb coupling (IC). We will first characterize IC for discrete bimanual aiming tasks in young control subjects. Based on this characterization, we will identify bimanual task conditions that elicit strong IC in control subjects and quantify and compare IC deficits for these conditions between individuals with LHD and RHD. Lastly, on the basis of the strong evidence supporting the role of the corpus callosum in mediating interlimb interactions, we will quantify corpus callosal microstructure, quantify associations of this measure with our measures of IC, and compare this relationship between chronic stroke survivors with LHD and RHD. Hypothesis: According to the Dynamic Dominance Hypothesis, the two hemispheres assume specialized but complementary roles in the two-component control of unimanual movement, with the left hemisphere responsible for feedforward mechanisms of control (in the early phase of movement), while the right hemisphere is responsible for feedback-mediated, end-point stabilization (in the late phase of movement).16 We hypothesize that interlimb coupling during bimanual tasks is influenced by hemispheric specialization. Thus, after a stroke, deficits in IC, will be dissociable between individuals with left and right hemisphere damage, with LHD exhibiting IC deficits in the early and RHD exhibiting IC deficits in the late phase of bilateral movements. Aim 1: Characterize interlimb coupling during discrete bimanual aiming tasks. Aim 2: Determine the influence of the side of stroke lesion on interlimb coupling. Aim 3: Investigate the relationship between corpus callosum microstructure and interlimb coupling. Studying fundamental neurobehavioral mechanisms and the identification of hemisphere-specific deficits of bimanual movements after stroke is a necessary first step toward the development of interventions to remediate these deficits. Successful accomplishment of these aims will advance our understanding of hemisphere-specific mechanisms, and by doing so, lay groundwork for the development of targeted training programs for stroke survivors with left- or right-hemisphere damage.